1998 Other Jaguar Models intermittent stalling

For the second time in 7 months my 98 Vanden Plas has just quit with no warning. Both instances only 0 throttle response was the first sign and neither was either hot or cold. The first time I let it sit overnight as the attempt to restart right away was not successful. Next day fine. The second was on the Interstate at cruise.I pulled over, waited two minutes and got an immediate but stumbling(for a second) start. Then fine.